This invention pertains to the preparation of copolymers of acrylic acid and nonionic surfactant acrylates and more particularly to their use as thickening agents for aqueous solutions and water/liquid hydrocarbon emulsions.
Various synthetic thickening agents composed of carboxylic acid monomers, such as acrylic acid, and a polyfunctional crosslinking monomer are known in the art. These interpolymers produce viscous, aqueous mucilages. However, these interpolymers rely upon the crosslinking monomer to achieve the desired aqueous thickening properties. U.S. Pat. Nos. 2,798,053, 2,858,281, and 3,426,004 disclose respectively polyallyl sucrose, polybutadiene and triallyl phosphate or phosphite esters as crosslinking monomers for polyacrylic acid to achieve interpolymers capable of producing viscous aqueous mucilages upon neutralization. U.S. Pat. No. 2,798,053 describes crosslinked copolymers of acrylic or methacrylic acid with minor amounts of vinyl, allyl and methallyl ethers of polyhydric alcohols having at least 4 carbon atoms and at least 3 alcoholic hydroxy groups, wherein the preferred polyalkenyl polyether monomers are polyallyl sucrose and polyallyl pentaerythritol containing an average of at least about 3 allyl groups per polyhydric alcohol. Similarly U.S. Pat. No. 3,426,004 describes crosslinked interpolymers of acrylic or methacrylic acids with from 0.1 to 2 weight percent of a polyallyl phosphate or a polyallyl phosphite ester such that at least 2 allyl ester functionalities and preferably 3 allyl ester functionalities are incorporated into the phosphate or phosphite monomer. U.S. Pat. No. 2,858,281 discloses the use of a polymeric crosslinking agent, polybutadiene, in forming the acrylic acid interpolymers.
U.S. Pat. No. 3,530,102 issued to Union Carbide Corporation describes terpolymers of maleic anhydride, vinyl alkyl ether and divinylbenzene as thickening agents.
U.S. Ser. No. 494,447 discloses ethylene-maleic anhydride interpolymers crosslinked with triallyl isocyanate to form a thickening agent.
U.S. Pat. Nos. 3,915,921 and 3,940,351 disclose synthetic thickening agents composed of acrylic acid and non-crosslinking comonomers. Alkyl acrylate esters having 10 to 30 carbon atoms in the alkyl portion are described as the non-crosslinking comonomers. Optionally a crosslinking agent is also disclosed, polyalkenyl polyethers.
The use of nonionic surfactant monomers and the preparation of synthetic thickening agents has been disclosed in U.S. Pat. Nos. 3,779,970 and 3,794,608.
Belgium Pat. No. 846,348 describes synthetic thickening agents composed of carboxamides and esters of maleic or fumaric acids which are useful as pigment printing thickeners. The maleic or fumaric acid is esterified with nonionic surfactants, such as, polyalkylene oxide adducts of alkyl alcohols, arylalkyl alcohols, and the like.
Polymers composed of a carboxylic acid monomer and one or more comonomers of which one monomer may be a multifunctional crosslinking monomer and in which the majority of the polymer is derived from the hydrophilic carboxylic acid monomer are typical of the synthetic thickening agents known in the art. Neutralization of the carboxylic acid-containing polymers in water produces gel-like polymers or mucilages exhibiting high viscosities. These polyelectrolyte polymers are useful as bodying and suspending agents in various applications such as pharmaceuticals, dentifrices, ointments, coatings, printing pastes, and the like. The rheological and solution properties of the neutralized polymers impart desirable characteristics to the various mucilage formulations. For example, the carboxylic acid-containing interpolymers described in several of the references delineated above produce highly viscous aqueous solutions which are thixotropic in nature and are readily formulated into useful creams, ointments, pastes, and the like. However, these high molecular weight interpolymers suffer the disadvantage of being sensitive to inorganic electrolytes, such as, sodium chloride. The ion-sensitive thickeners do not effectively maintain their viscosity and drastic viscosity losses in the presence of inorganic electrolytes are observed. Such ion-sensitivity is deleterious to the performance of these thickeners when they are included in formulations such as latexes, food preparations, cosmetic creams, ionic detergents, and dye pastes. One attempt to overcome this deficiency was disclosed in U.S. Pat. Nos. 3,915,921 and 3,940,351 wherein polymers composed of acrylic acid and long-chain alkyl acrylates were described as being less electrolyte sensitive than other carboxylic acid interpolymers of the prior art. However these synthetic thickeners are less efficient thickeners than the interpolymers and require the addition of a crosslinking monomer to attain high solution viscosities. Incorporation of the crosslinking agent reduces the electrolyte compatability far below the compatabilities of polymers without the crosslinker.
Polymers composed of carboxylic acid monomers and crosslinking monomers are used as thickeners for water-hydrocarbon emulsions. Water-hydrocarbon emulsions used in the preparation of printing inks, pigment printing pastes, and the like include synthetic thickeners which serve to increase the paste viscosity and to impart thixotropic properties to the formulation. Prior art polymers function adequately but the water-hydrocarbon emulsion viscosities are less than the viscosities obtained in water solutions. This requires the addition of more thickener to the paste to obtain the viscosities exhibited in an all aqueous system. Thickeners which maintain or exhibit an increase in the water-liquid hydrocarbon emulsion viscosity compared to the aqueous viscosity would permit the formulator greater latitude in the preparation of printing inks and pastes. In addition, the use of less thickener imparts a more thixotropic rheology to the formulation, a property required for the proper application of the printing ink or paste to the medium being printed.
It is therefore an object of this invention to provide thickening agents with improved salt tolerance.
It is another object of this invention to provide thickening agents which have a high thickening efficiency in aqueous solutions.
It is still a further object of this invention to provide thickening agents which have a high thickening efficiency in water-liquid hydrocarbon emulsions.